its seal function can still work Plate Spares for Alfa Laval Gasket Plate Heat Exchangers Stainless Steel /Ni /Ti Plates with EPDM /NBR /VITON Gaskets US 10-30 / Piece 10 Piece/Pieces (Min.Order) ALFA ...

Then install a foam gasket under the cover plate. Air is probably leaking under the bottom plate of the walls. You may be able to seal this by caulking under baseboards. In the worst cases ...